void insertion_sort(int arr[], int len) {
        int i, j, key;
        for (i = 1;i < len;i++)
        {
                key = arr[i];
                j = i - 1;
                while ((j >= 0) && (arr[j] > key))
                {
                        arr[j + 1] = arr[j];
                        j--;
                }
                arr[j + 1] = key;
        }
}